1. Field of the Invention
This invention relates to a control system including an evaporative emission control system for an internal combustion engine, which is adapted to purge evaporative fuel generated from a fuel tank into the intake system.
2. Prior Art
Evaporative fuel purged into the intake system of the engine affects or has influence on the air-fuel ratio control. Therefore, a technique (system) has been proposed, e.g. by Japanese Provisional Patent Publication (Kokai) No. 63-57841, for taking the influence of the purge into account in correcting a basic fuel injection amount, i.e. a basic amount o fuel to be supplied to the engine by injection, by the use of an air-fuel ratio correction coefficient determined based on the concentration of oxygen present in exhaust gases.
However, the proposed system detects purge of evaporative fuel, and performs purge-dependent correction of the basic fuel injection amount only while purging of the evaporative fuel is being performed.
That is, although the basic fuel injection amount is corrected when purging of evaporative has great influence on the air-fuel ratio control, the correction of the basic fuel injection amount dependent on purging of evaporative fuel is stopped when the purge of evaporative fuel is interrupted, considering that purged evaporative fuel does not affect the air-fuel ratio control any longer.
Therefore, the proposed system does not take into consideration the fact that a portion of purged evaporative fuel stays within a purging passage after purging is stopped, and is drawn into the intake system, though in a small amount.
If purging of evaporative fuel having high concentration is stopped, the influence of evaporative fuel staying within the purging passage can have a significant influence on the air-fuel ratio control, degrading responsiveness and stability thereof.
Similarly, when purging off evaporative fuel is resumed, it takes some time for the purged evaporative fuel to flow from a purge control valve through the purging passage into the intake system to have actual influence on the air-fuel ratio control. However, the proposed system does not take this delay into any account.